Processing cellulose nitrate



is soluble in water in all proportions.

id Stats PROCESSING CELLULOSE NITRATE Arthur W. Sloan, Washington, D.C.,and David J. Mann,

Wharton, NJ, assiguors to Atlantic Research Corporation, Alexandria,Va., a corporation of Virginia No Drawing. Application August 13, 1954Serial No. 449,777

17 Claims. (Cl. 260223) content cellulose nitrate (12.413.4% nitrogen)are de scribed in Olsen et al., US. 2,027,114, and Shaefer, US.2,160,626. In the former patent, a colloid, such as starch, is used toobtain sphere formation and the products are highly porous, withspecific gravities ranging from about 0.25 to 0.5. In the latter patent,a solute such as sodium sulfate, is added to the aqueous phase of theemulsion to increase density of the cellulose nitrate spheres. It isstated that specific gravities as high as 0.8 to 1.0 may be obtained.However, in view of actual specific gravity of high nitrogen contentcellulose nitrate of 1.58 to 1.66

depending upon degree of nitration, it is evident that a product havinga specific gravity of 0.8 to 1.0 possesses a high degree of porosity.For some uses, considerably denser spherical particles are required. Anadditional disadvantage of these processes stems from the fact that thesmallest particle produced is about 6 mils of 150 microns and these areobtainable only as a screened fraction of a batch containing a largeproportion of considerably larger spheres. Thus these processes cannotmeet a requirement for cellulose nitrate spheres smaller than 6 mils andeven the smaller sizes produced by these methods constitute only aportion of a given production.

The object of this invention is to provide a process for making small,substantially non-porous, spherical particles of cellulose nitrate ofhigh nitrogen content, namely cellulose nitrate containing more than 12%nitrogen.

Other objects and advantages will become obvious from the followingdetailed description.

We have discovered that high nitrogen content cellulose nitrateparticles having the desired characteristics of size, sphericity andsubstantial non-porosity may be obtained when the cellulose nitrate inspecified concentration is dissolved in an organic solvent characterizedby certain essential properties and the resulting lacquer is dispersedwith vigorous agitation in specified amounts of water in the presence ofcertain colloids together with Water-soluble salts or water-solublepolyhydroxy compounds to form an oil-in-water type emulsion. In somecases it is also desirable to introduce a polar-type, surface-activeemulsifying agent.

The cellulose nitrate solvent may be a single solvent which ismoderately soluble in water, a mixture of solvents, the components ofwhich are moderately soluble in water, or a mixture of solvents, atleast one component of which is moderately soluble in water and anothercomponent of which is infinitely soluble in water. By moderately solubleis meant a solvent which is soluble in water at least to the extent ofparts per 100 parts of water at C. but is not infinitely soluble. Byinfinitely soluble is meant a solvent which Maximum solubility in waterof the cellulose nitrate solvent should be Infinitely water-solubleco-solvents include the lower aliphatic alcohols such as methyl, ethyland propyl alcohols, acetone, methyl lactate, ethyl lactate, anddioxan-1,4.

Where co-solvent mixtures are used, it is not essential that each of thesolvent components be a good solvent' for the cellulose nitrate so longas they possess good solvent properties when in admixture. Diethyl etherand' the lower aliphatic alcohols, for example, though poor solvents forcellulose nitrate per se, possess excellent cosolvent properties. It isdesirable that the infinitely soluble component of a mixed cellulosenitrate solvent possess the ability to reduce viscosity of the lacquer.Methanol, ethanol and acetone are particularly effective in this regard.r

We have found that particles having the desired characteristics cannotbe obtained with a cellulose nitrate solvent which is substantiallyinsoluble in water, namely soluble in water to the extent of less thanabout 5 parts per 100, or which is excessively soluble. The watersolubility must be sufiicient so that when the lacquer par ticles aredispersed in water, the solvent at and adjacent to the surface dissolveswith sufiicient rapidity in the water to permit some hardening orsetting of the particle surface and thus eliminates or markedly reducesthe surface tackiness to the point where such surface tackiness will notcause agglomeration. On the other hand, elution of the solvent shouldnot be so rapid that the surface sets into a hard, non-plastic conditionbefore surface tension forces can effectively shape the particles intothe desired spherical form. Premature excessive hardening of theparticle surface also causes porosity since the nonplastic surface. doesnot permit adequate shrinkage to compensate for removal of solvent fromthe interior of the particle. With a cellulose nitrate solvent ofexcessive Water-solubility, porosity may also be caused by migration ofwater into the particle because of the mutual solubility of water and ahighly water-soluble solvent. As aforementioned, the water-solubility ofthe cellulose nitrate solvent, whether single or mixed, should be within'a range of about 5 to parts per parts of water at 20 C. and preferablyabout 5 to 40 or 50.

We have found that to obtain spheres of the desired small size,concentration of the high nitrogen content cellulose nitrate in thelacquer should not exceed about 10% by weight. 7.5 the high nitrogencellulose nitrate are highly viscous and are comminuted with difiicultyto produce particles of generally excessive size. There is no criticallower limit of cellulose nitrate concentration in the lacquer other thanthat dictated by economic expediency. Good results are obtainable, forexample, with concentrations as low as 2%. This, however, requires theuse of large amounts of solvent and large operating equipment relativeto the amount of cellulose nitrate processed.

Choice of the particular solvent influences to some degree the cellulosenitrate concentration in the lacquer. Viscosity of the lacquer varieswith different solvents and the concentration of cellulose nitrate maybe varied accordingly.

Optimum concentration is about 5 to Lacquers containing more than about10% of by' volume is -particulz'u ly"'goecl'; However,- this maybevari'edso long astotalsolubilityof the mixedsolvent doesnot'be'comeexcessiv'ei' A p Choice of solvent'is also inftnenc t'c so'niefextent bytheparticulaj'r' colloiding'l agent employed: The protectiv'ei colloidmust not be excessivly s tendj tdfor'mja watei inioiltype"emulsiohlThifs"sitiiation canlbehandled by employinga eoltei whic is not high 1ysoluble in'th e specific solvent or by avoidihg the *u'se of solvents jwhich tend to dissolve the particular colloid I Thecellulos'e'nitrate'lacquer i'sihixd-witli water'in the presence ofasuitable colloidinga'g'ent and aWater-soluble salt or polyhydroxyjcompoundwi thvigorousagitation to form 'a'dispersio'n ofsmallispheric'allac'quer particles with therwater asthe continuous-phaseThecolloid-an'd salt' are preferably introduced intothe Water prior tomixing:-

The dispersion and a'git'ation may be accomplished byany suitablemeansas; for examplep inm hom'o'genizer or other suitable agitatingdevice; Thede'gree of agitation is one of'the"factorsinfluencing'particle size; In general, the more vigorous theagitation;the smaller are the particles;

The amount of water employed indispersing-the cellulose nitratelacquer'isan important factor in determining particle size; Particlesize is-a function of the lacquer/ Water. ratio'in asmuchasincreasingtheamount ofwater increases particlesize; Thns'thequantity ofwaterused in emulsification is determined 'in' sorne measure by 'the'particle "size desiredf' Thefminimum'airrount of 'Water' is governed Iby' the lacquer/Water r'atidrequir'd to permit formationofthe-requisitebiPin Watentypeemulsion; If

excessive water' is? employed, the particles become over= sizeandmay'also 'become"irre'gular' and porous, appar entlybecause the organicsolvent" dissolves in the water phase"vvitlr'excessiverapidity s'othat'the surfa'ceofthe' particles hardens into a'non-plasticconditionbefore'ade' qu'ate'comminution or contraction-into spheres; Ingeneral,the'maximum'amount of water which gives satisfactory-results in'termsofdesired'particle characteristics isabout" 100% by volumebased on thevolume of organic'solvent'andpreferably about SOto 75%;

We'have'found'th'at particlechar'acteristics such as size and densityare greatly 'influencedby theparticular'colloid employed: Non-porousparticle's withinthe" desired size range canbeobtai ned with thefollowin'g' colloiding' agentsi methyl -cellulose; casein, thecon'densation' prod uet of polyvinyl 'niethyl'etheranfdiinaleic anhydiide',gel-' ati'ri, agar-agar, polysodiufn aerylatej polyvinyhalcohol;andalginate's.

Thecolloidingfage'nt 'mu'stbeprefe'rentially sample in" water ratherthan in theorganic solvent"to"avei'd format-f tion-"of ajwater-imoilsystem; Alth'ough"the.afo'rementioned'colloids are'normally hydrophilic,certainones may be excessively soluble in a particular organic solvent.

Methyl cellulose, for 'example,cann ot beemployed 'With" ethyl aeetatebecause'of its hi gh' solubility in"this solvent;

although itfunctionswell' withother' solvents such as methylethyl'ketone/acetone. It is "essential, therefore,

to employ organic s'olvent-c'olloid"'systems ofil'o'w mutual:solubilityrela'tive' tothe "solubility of 'the colloid in the water. Thenitrornethane polyvinyl methyl 'etlietf-n'ialeib' I olublefin'thefcellii? lose? nitrate sen/ens since; ptherwise, the'sys'tem would 4I anhydride system, for example, is excellent because of theinsolubility of the colloid-inthis solvent;

The colloiding agent forms a colloidal solution with the water, thusincreasing the viscosity of the water phase, and also surrounds thelacquer particles with a protective coating. These factors stabilize theemulsion by reducing tendency of the particles to co'alesce,particularly during stripping ofthe solvent. This is important since theparticles must bem'aintained in a state of dispersion until surfacetackines's has been substantially eliminated and hardening hasprogressed to thepoint-where' the particles will nolongeraggloiriei'a'te:

The amount-of colloiding agent employed is determined by severalfactors. Primarily, it should be sutficient to produce substantialincreasein the viscosity of the water phase and to coattheparticles,thuspr'oviding adequate stabilization of the emulsion during processing.Generally speaking, the higher the molecular weight of the colloid, thelesswill be "required. Thecolloid" 'is-' also a factorin controlling 1particle" siZe since increasingcon centration tends to reduce-particlesize? There is no critical upper limit to the amount of colloid employedother thanpractical considerations "such as desired'pa'rticle size andease of-Washing;- The more co'lloid prese'nt, the more Washingisre'quired for its 1 removal.

Colloid-organic solvent systems 'which we have found particularlysuitable for our purpose include casein -plus" ethyl acetate, methylcelluloseplusmeth'yl acetate, methylethyl ketone/ acetone or methylethyl ketone/methanol; polyvinyl methylether ma'leic" anhydr'ide plusnitro methane or ethylacetate, al inates plus ethyl acetate; and gelatinplus ethyl; acetates Themethyl cellulose is preferably of the highermolecnlar weiglre variety, namely" one having a minimum centipoisevalne'of about 400 and preferably about 1500 to 4000 or higher.

It is essential that a suitable" water-soluble' -salt' or" an organicpolyhydroxy "compound be included in the water phase of the emulsionsystem. Iti s apparently necessary for the proper functioning of-theprotectivecol loid. Without the "additiorr of such ce'nipennds;the"par' ticles formedare non spheric'al and 'qversizex Thes'alt orpolyhydroxy compound prevnts the inversion-ne hew which frequentlyoccurs when the "en'1uls'ion is heated-'-'to distillation temperaturetorem'ov'e the organic? solvent;

It may be; alsoythat these 'arlditives exert 'a' stabilizi'ng efifect bycausing hydration ef the colloid "and th'us preventing undue penetrationof thecolloid 3 into the lacquer particle',* an'd, in' the case of-thesalts, by inducin'g achar'ge on*the' surface of-"the'colloid-envelt'l'ped particle which measure; determined by= the'parti'c'sular colloidm'sed-in the emulsionsystem;- All of'thecolloidin'g' a'gentsexcept methyl cellulose functionwell with salts of 1any valence, preferably mono'valent 01 "divalent salts, as, for example,sodiunr chloride or sodium sulfate? I Meth'yl celliil'o'sei however;tolerates only i nieneva1ent salt's sueh" 1 as the alkalimetaland-ammoninin halides; ny menovalent salt is meant one inWhich'bdth the at! 'ri= 'andanion are} By divalent saltislm'ea'ntone' inwhich at monovalent. least one ion is divalent In generallinorg'ahies'alts having monovalent' cations are} preferred, -th'e'-'-alkali'-nietalsalts being mostdesirable-'- The saltmust be employed in an' amountless than" tha't' whi'cli' will cause reci itation of" the colloid or asal ti'n'g out effect. In*general;the'lovver fthe"molecular; weight ofthe-"colloid, thegfeaterthe amount of salt which itwill tolerate.Degreeof salt 'toleration-alsd centrations' "the salt isi'not effective"since the resulting" particles tend to be oversize and non-spherical.This minimum amount varies with the particular salt. In general, theminimum concentration for the monovalent salts is about 6.5% based onthe weight of the cellulose nitrate and for divalent salts, such assodium sulfate, about 13%.

Additives other than salts which we have found to perform satisfactorilyare water-soluble polyhydroxy compounds such as sugars, glycerin andglycols such as ethylene glycol. In general, a minimum of about 6.5% onthe cellulose nitrate is desirable for satisfactory performance.

In some-cases, it may be desirable, though not essential, 'to include inthe system a polar-type, surface-active emulsifying agent which producesa marked lowering of interfacial tension and which, unlike the highermolecular weight colloiding agent, does not produce any appreciable.

nents of the system and which is substantially soluble' in water, namelypossesses a sutliciently high hydrophilelipophile balance to prevent itsbeing drawn into the organic solvent and converting the emulsion into awaterin-oil system, may be employed, such as alkyl sulfatesorsulfonates, alkylaryl sulfonates, alkali metal soaps, al- 1 kali metaland ammoniumsalts of perfiuoro acids, alkali metal salts ofsulfosuccinic acids, sulfonated oils including sulfonated vegetable oilsand sulfonated hydrocarbon oils, polyglycols and the like. Themoderately active types of emulsifying agents such as the sulfonatedvegetable oils as, for example, sulfonated castor'oil,

sulfonated coconut oil and the like, sulfonated hydrocarbon oils as, forexample, sulfonated petroleumfractions, alkali metal fatty acid soaps,polyglycols such as polyethylene glycol and polypropylene glycol, andthe like, are especially satisfactory. The polyglycols, in addition totheir dispersing action, also may be advantageous as coupling agents,namely as agents which increase solubility of the colloid or the organicsolvent in water.

The amount of surface-active emulsifier is not critical but should besufficient to promote'the desired rapid emulsification and comminutionof the particles. As little as about'0.01 to 0.25% based on the waterphase may be adequate. The amount may be increased to'as much as 5 to10% in some cases. Concentrations of emulsifier in the range of about0.01 to 2% are generally satisfactory. The emulsifier may be added tothe water or to the lacquer phase.

After emulsification is completed, the organic solvent is removed fromthe dispersed particles by distillation or by elution. Ineither case,the emulsion should be maintained in a state of'continuous vigorousagitation.

Distillation is accomplished by heating the emulsion to or near theboiling point of' the organic solvent. If the distillation is conductedat atmospheric pressure, it is desirable that the solvent or the leastvolatile component of a mixed solvent has a boiling point below 100 C.to maintain stability both of the cellulose nitrate and of the emulsion.In many cases, it may be desirable to distill under reduced pressures,particularly if the boiling point is above 100 C. i

vAnother effectivemethod for removing the organic solvent is by dilutingthe emulsion with water in amount.

suflicient substantially completely to dissolve the solvent out of thecellulose nitrate particles. Since it is desirable to' maintain theeffective salt or polyhydroxy compound concentration throughout thedisperse phase of the particles, it is preferable to include thesesolutes in the elution water prior to dilution of the emulsion. Thetotal amount of water should be in excess of the theoretical amountrequired for solution of the organic solvent,

preferably in substantial excess. After removal of the organic solvent,the cellulose nitrate particles are separated from the water, washedwith water and dried. Removal of the colloid may require severalwashings. In general, the smaller the particles, the more water washingsare required.

The cellulose nitrate particles prepared according to our process arespherical and may be obtained in sizes as, small as 1 micron or less indiameter. The particle size generally ranges up to about 10 or 30microns. This is the preferred size range. Depending upon the specificcomponents and concentrations employed in the process;

particle size may range up to about microns. Ingeneral, products inwhich the average particle diameter is above about 50 microns aremarginal. In other words, it is preferable that the size distribution ofthe particles by number be such that the maximum average size is about50 microns. Since all of the particles in a given production batch areobtainable in the desired s mallsize range, there is no necessity forfractional screening or reworking of excessively large particles.

Density of the cellulose nitrate spheres is high. Aver age density ofthe spheres is about 1.49 to 1.54 with a minimum of about 1.4 ascompared with published cellulose nitrate densities of 1.58 to 1.66.

The small, dense, spherical particles of cellulose nitrate are highlysuitable for use in the manufacture of smokeless powder charges andpropellants in any desired and conventional manner. They are especiallyuseful, however, in that they can be suspended in a nonvolatileplasticizer to form homogeneous, stable fluid slurries which may bepoured as coatings or films without requiring the addition of water or avolatile solvent and may be molded into objects of any desired shape andsize without the application of high temperatures and pressures. V V

Nitroglycerin is readily incorporated with the cellulose nitrateparticles by introducing it into the lacquer. It may be added with theorganic solvent prior to solution of the cellulose nitrate or it can beadded to the cellulose nitrate-solvent solution. Stabilizing agents suchas diphenyl amine, lecithin, ethyl centralite and the like can similarlybe added.

EXAMPLE I 20 grams of cellulose'nitrate (12.6% N) were dissolved in 200ml. ethyl acetate to form a clear lacquer. 8 grams casein, 8 grams Na SOand 0.3 gram ethyl centralite were dissolved in ml. water. The aqueoussolution was added to the cellulose nitrate lacquer in a. homogenizer.The emulsion was agitated vigorously for about 5 minutes and then washeated to about 77 C. to distill off the ethyl acetate from thedispersed spherical particles. Vigorous agitation was maintained duringdistillation. The product was washed with water 3 times, filtered,washed again with water and dried. The product was in the form ofspherical particles ranging in size from 2 to .20 microns with anaverage size of 12 microns and having a density of 1.54.

EXAMPLE II 10 grams of cellulose nitrate (12.6% N) were dissolved in 200ml. ethyl acetate to form a clear lacquer. 8 grams gelatin (Knox) and 14grams Na SO were dissolved in 150 ml. water. The aqueous solution wasadded to the cellulose nitrate lacquer in a homogenizer. The emulsionwas agitated vigorously for about 5 minutes. The organic solvent wasdissolved out of the spherical particles by flooding the emulsion withabout 4 volumes of water containing about 2% of the salt under continuedagitation. The product was filtered, washed with water about 3. timesandthen dried. The spherical particles ranged inlsize from 1 to 10microns andhacl a density of about, 1.49. -therqexamples l t e i psuinve o ar marized in Table I. The particles in' all cases were waterphase, removinglth'e organic solvent from the} solventg the cj'illoidingagent being. present: amount spherical. persed particles bydflutmgtheemulsion with suflicient Table l Cellulose nitrate Solvent, ml. Colloid,grams Other additives Solute; grams Wa ter, 812c PercentN g.

12.6;' 20' Ethyl acetate',20fl' Casein?" Ethyl centrallte;0.3-2 NaISO160- 2 40, av. 20. 12.6. 20, ECaseln, Ethyl eentrallte, 0.8. NB SO,8..--.- 150 2-35,av.15.

Glyceryl monorieino e-' 1 a. g; A 20 rln 7 do Ethyl. centralite, 0.3g.;, Na sqz, 8; 150' 2-40, av.2,0. A Polyethyleneglycohfig p l v 20- Ydov Ethyl centrallte;0.3'g ,BuganS 15D !0-'40,av.2D; 20 d do Ethflylgn yi 150 2-30;av.

. c 20 r. i; win"- Glycerimfilu. 150 2 -15. 20 Casein,8; Poly inyl medNa sOn 1 50 2e30,av. 15.

ghiygetlher-maleie anhyr 9 H. 20. Ethyl zibcetat e, 180; Etha- Casein,N.a1S0, R 15 0' 2-30, ay. l5.' o, 20' -Ethyl acetate, 170; Acea--- NaiS0,8. 150 1 1. a'v. 18'

tone, 4 I v and 2-6. 20 n a tate, 17o; Ethyl an m Na,sor,s 1502-20,'av.15.

- i e er, 20;: Ethyl aeetatefl o Na S0 ,4 150 -40, av. 20. 20 Ethylacaedtate', 170; Ethyl 'Hexaleue gly- 150 2-30,av. 15. W er, 00,." 10,.Ethylacetate, do v Na;S0 150, 2:15, av. 8. (in I fln Ethyl centralite,0.3'g.;' NaySOl, 8; 2- 150' 2 25,av."10.

Bolyethlleneiglycol, 0.5 g.'. 2 I W Methyl ethyl ketone, 170;. .Methylcellulose, 4,000 Ethyl centralite, 0.3. g.; NaCl,4 150 240. e ancps:,;2.1: Turkey red oll,1.6 g." 20 Methyl ethyl ket0ne,170;' Iln NaCl,150' 1-10. Acetone, 30. 20' do fin dam NaCL4 150 1-20. 10 Methylacetate,200.' Methyl 0 1111 5 1,50 ,Ethyl'centralltmofs g.'..-.. Na;SO,4150' .1;

9 w 10 Ethyl acetate, 200; A gergar; 1 10 do Agar-agapfl 10. Agar-agar,2 14 Polyvinyl alcohol, 14 Polyvinyl alcohol, 4 10 Gelatiu,- 10'Gelatin,'fi 14.1 r 10 10 10 Gelatin, 8'. V 20 Gelatinfn dn 10Gelatin,18;:Alglnate50.5.- Diphenyl amine,0.2.g 10 .Al natal d. H 10-A'lglnate; 1 Ethyl centrallte,0.2"g 10" :Algmateym do 10., .Polysodiumacrylate, 3.--- d 7 p 20 40 10 -Po1yvinyl'metlryletherdo Na SO ,4 150'1-10'. rnaleic anhydride,4. 20 Nltromethane,2 00 Polyvinyl'methyletherrln Na;SO ,12.'.-- 150 2-20.

maleic anhydride, 6.

1 Kelcolold LV.

Although this 'invention has been described yvith reference' toillustrativeembodimentsthereof, it yvill be: apparent-to those skilledin the art that it may be embodied in other forms but within the scopeof the appended claims.

1. A 'process for making small, substantially nonporous, substantiallyspherical particles of cellulose n itrate having a nitrogen content ofmore than 12%, the :particles beingcharacter-ized by diameter of about100 microns which compriseedissolving to about 10% of said cellulosenitrate in an organic solvent which is moderately' solubleiri water tothe extent of at least a'bout' fi parts-per; IOU-parts ofwaterat 20C.,...anyi componentof said. solvent having a minimum waterrsolubilityofat least about 5 ,parts, dispersing-the cellulose-nitrate; solutioninwater .in thefpresence of a colloiding ragent.selected from? the groupconsisting of methyl CEHUIQSBJHCHSCH'I; polyvinylsmethyl ether-maleicanhydride, gela'tin,r.agareag'ar;-.polysodium ;acrylate-, -polyvinyl:alcohol;=-;and alginates; and ;a {solute selected fromthe'groupaconsistingof waterj-solublewalts; and;watersolublepolyhydroxy. compounds; the :waterbeingpresent illiamdllllt sufliciei'itto form an ioilzin watertype emulsion water to dissolvethe organicsolvent out 'lOf the dispersed cellulose'nitrate' particles, saidwatercontaining dissolved' infthe water employed for dispersing:thecellulose nitrate solution is a v'va'ter-soluble inorganic salt inan 'amount comprisingat" least about 6.5 by" weight basedon the'cellulose -nitrate and' less than that which causesprecipitation';of-tlie'colloiding agent and the sdimepres injin'thewater employed for dissolving the organic solvent outof the dispersedcellulose nitrate .particlesis' a water soluble inorganic salt.

4. The process of c'la irn' z 'inwlii'ch the" solute present inthewateremployed for dispersing the cellulose'nitr a'te' solution is a vvatersolubleinorganic salt .an amount comprising at least about. 6.5% byWeigh't-fbased on' the cellulose nitrate and less than that which causes pre-9 cipitation of the colloiding agent, and the solute present in thewater employed for dissolving the organic solvent out of the dispersedcellulose nitrate particles is a watersoluble inorganic salt.

5. The process of claim 1 in which the organic solvent has a maximumwater-solubility of about 50 parts per 100 parts of water at 20 C. andcomprises at least two components, one of said components beingmoderately soluble in water to the extent of at least about parts per100 parts of water at 20 C. and another of said components beinginfinitely soluble in water.

6. The process of claim 2 in which the organic solvent has a maximumwater-solubility of about 50 parts per 100 parts of water at 20 C. andcomprises at least two components, one of said components beingmoderately soluble in water to the extent of at least about 5 parts per100 parts of water at 20 C. and another of said components beinginfinitely soluble in water.

7. The process of claim 3 in which the salt is one, the cation of whichis selected from the group consisting of alkali metal and ammonium andthe anion of which is selected from the group consisting of halide andsulfate.

8. The process of claim 4 in which the salt is one, the cation of whichis selected from the group consisting of alkali metal and ammonium andthe anion of which is selected from the group consisting of halide andsulfate.

9. A process for making small, substantially nonporous, substantiallyspherical particles of cellulose nitrate having a nitrogen content ofmore than 12%, the particles being characterized by maximum diameter ofabout 100 microns which comprises dissolving up to about of saidcellulose nitrate in an organic solvent which is moderately soluble inwater to the extent of at least about 5 parts per 100 parts of water at20 C., any component of said solvent having a minimum water solubilityof at least about 5 parts, dispersing the cellulose nitrate solution inwater in the presence of methyl cellulose and a monovalent water-solublesalt, the water being present in amount suflicient to form anoil-in-water type emulsion and up to about 100% by volume based on theorganic solvent, the methyl cellulose being present in amount sufficientto increase substantially the viscosity of the water phase, the saltbeing in an amount comprising at least about 6.5% by weight based on thecellulose nitrate and less than that which causes precipitation of thecolloiding agent, removing the organic solvent from the dispersedparticles by diluting the emulsion with suflicient water to dissolve theorganic solvent out of the dispersed cellulose nitrate particles, saidwater containing dissolved monovalent, water-soluble salt, andseparating the particles from the water.

10. The process of claim 9 in which the organic solvent is a mixture ofmethyl ethyl ketone and acetone and the salt is sodium chloride.

11. A process for making small, substantially nonporous, substantiallyspherical particles of cellulose nitrate having a nitrogen content ofmore than 12%, the particles being characterized by maximum diameter ofabout 100 microns which comprises dissolving up to about 10% of saidcellulose nitrate in an organic solvent which is moderately soluble inwater to the extent of at least about 5 parts per 100 parts of water at20 C.,

particles by diluting the emulsion with suflicient water water-solubleinorganic salt, and separating the particles from the water.

12. The process of claim 11 in which the organic solvent is ethylacetateandthe salt is one, the cation of which is selected from the groupconsisting of alkali metal and ammonium and the anion of which isselected from the group consisting of halide and sulfate.

13. A process for making small, substantially nonporous, substantiallyspherical particles of cellulose nitrate having a nitrogen content ofmore than 12%, the particles being characterized by maximum diameter ofabout 100 microns, which comprises dissolving up to about 10% of saidcellulose nitrate in an organic solvent which is moderately soluble inwater to the extent of at least about 5 parts per 100 parts of water at20 C., any component of said solvent having a minimum Water solubilityof at least about 5 parts, dispersing the cellulose nitrate solution inwater in the presence of polyvinyl methyl ether-maleic anhydride and awatersoluble inorganic salt, the water being present in amountsufficient to form an oil-in-water type emulsion and up to about 100% byvolume based on the organic solvent, the polyvinyl methyl ether-maleicanhydride being present in amount sufiicient to increase substantiallythe viscosity of the water phase, the salt being in an amount comprisingat least about 6.5% by weight based on the cellulose nitrate and lessthan that which causes precipi tation of the colloiding agent, removingthe organic solvent from the dispersed particles by diluting theemulsion any component of said solvent having a minimum water solubilityof at least about 5 parts, dispersing the cellulose nitrate solution inwater in the presence of casein and a water-soluble inorganic salt, thewater being present in amount sufiicient to form an oil-in-water typeemulsion and up to about 100% by volume based on the organic solvent,the casein being present in amount suflicient to increase substantiallythe viscosity of the water phase, the salt being in an amount comprisingat least about 6.5 by weight based on the cellulose nitrate and lessthan that which causes precipitation of the colloiding agent, removingthe organic solvent from the dispersed with sufficient water to dissolvethe organic solvent out of the dispersed cellulose nitrate particles,said water containing dissolved, water-soluble inorganic salt, andseparating the particles from the water.

14. The process of claim 13 in which the organic solvent is nitromethaneand the inorganic salt is one, the cation of which is selected from thegroup consisting of alkali metal and ammonium and the anion of which isselected from the group consisting of halide and sulfate.

15. The process of claim 13 in which the organic solvent is ethylacetate and the inorganic salt is one, the cation of which is selectedfrom the group consisting of alkali metal and ammonium and the anion ofwhich is selected from the group consisting of halide and sulfate.

16. A process for making small, substantially nonporous, substantiallyspherical particles of cellulose nitrate having a nitrogen content ofmore than 12%, the particles being characterized by maximum diameter ofabout microns, which comprises dissolving up to about 10% of saidcellulose nitrate in an organic solvent which is moderately soluble inwater to the extent of at least about 5 parts per 100 parts of water at20 C., any component of said solvent having a minimum water solubilityof at least about 5 parts, dispersing the cellulose nitrate solution inwater in the presence of gelatin and a water-soluble inorganic salt, thewater being present in amount sufiicient to form an oil-in-water typeemulsion and up to about 100% by volume based on the organic solvent,the gelatin being present in amount sulficient to increase substantiallythe viscosity of the water phase, the salt being in an amount comprisingat least about 6.5% by weight based on the cellulose nitrate and lessthan that which causes precipitation of the colloiding agent, removingthe organic solvent from the dispersed particles by diluting theemulsion with sufiicient water to dissolve the organic solvent out ofthe dispersed cellulose nitrate particles, said water containingdissolved, water-soluble inorganic salt, and separating the particlesfrom the water.

17. The process of claim 16 in which the organic solvent is ethylacetate and the inorganic salt is one, the cation of which is selectedfrom the group consisting of 2,891,055 1 1; 12. alkali metal andammonium. and'the anion of which is 2,169,626 Sphagfer May 30, 1939Z0273 Olsen at all. Jam, 1936 53; pp. 92-96 (Nb;12;December 1-946)

1. A PROCESS FOR MAKING SMALL, SUBSTANTIALLY NONPOROUS, SUBSTANTIALLY SPHERICAL PARTICLES OF CELLULOSE NITRATE HAVING A NITROGEN CONTENT OF MORE THAN 12% THE PARTICLES BEING CHARACTERIZED BY MAXIMUM DIAMETER OF ABOUT 100 MICRONS WHICH COMPRISES DISSOLVING UP TO ABOUT 10% OF SAID CELLULOSE NITRATE IN AN ORGANIC SOLVENT WHICH IS MODERATELY SOLUBLE IN WATER TO THE EXTENT OF AT LEAST ABOUT 5 PARTS PER 100 PARTS OF WATER AT 20* C., ANY COMPONENT OF SAID SOLVENT HAVING A MINIMUM WATER SOLUBILITY OF AT LEAST ABOUT 5 PARTS, DISPERSING THE CELLULOSE NITRATE SOLUTION IN WATER IN THE PRESENCE OF A COLLOIDING AGENT SELECTED FROM THE GROUP CONSISTING OF METHYL CELLULOSE, CASEIN, POLYVINYL METHYL ETHER-MALEIC ANHYDRIDE, GELATIN, AGAR-AGAR, POLYSODIUM ACRYLATE, POLYVINYL ALCOHOL, AND ALGINATES, AND ASOLUTE SELECTED FROM THE GROUP CONSISTING OF WATER-SOLUBLE SALTS AND WATERSOLUBLE POLYHYDROXY COMPOUNDS, THE WATER BEING PRESENT IN AMOUNT SUFFICIENT TO FORM AN OIL-IN-WATER TYPE EMULSION AND UP TO ABOUT 100% BY VOLUME BASED ON THE ORGANIC SOLVENT, THE COLLOIDING AGENT BEING PRESENT IN AMOUNT SUFFICIENT TO INCREASE SUBSTANTIALLY THE VISCOSITY OF THE WATER PHASE, REMOVING THE ORGANIC SOLVENT FROM THE DISPERSED PARTICLES BY DILUTING THE EMULSION WITH SUFFICIENT WATER TO DISSOLVE THE ORGANIC SOLVENT OUT OF THE DISPERSED CELLULOSE NITRATE PARTICLES, SAID WATER CONTAINING DISSOLVED SOLUTE SELECTED FROM THE GROUP CONSISTING OF WATER-SOLUBLE SALTS AND WATER-SOLUBLE POLYHYDROXY COMPOUNDS, AND SEPARATING THE PARTICLES FROM WATER. 